"Obviously, if these destructive events are 10 times more common than was suspected before, then our disaster response planning, town planning and our approach to coastal development all need to take that into consideration," Dr Nott said.

Instrument-measured records of tropical cyclone intensity only go back 100 years, but the new study determines the intensity of cyclones over the past 5000 years by looking at coral deposits left along a 1500km stretch of the Great Barrier Reef.

On island and coastal sites in northern Queensland, cyclones create ridges by throwing coral and shell debris high above the usual tidemark.

"We've taken the estimated wave size and storm surge measurements from past cyclones, and in effect run those models in reverse, to determine what size cyclones would be required to create the ridges," he said.

The study showed that the last super-cyclone -- a category 5 cyclone, with wind speeds of up to 300kmh -- came 50 years before European settlement of the area, in about 1820. If it hit Cairns today, the resulting marine inundation would swamp the city's esplanade in two metres of water.

Cairns, on Australia's north-east coast, is built to withstand a cyclone as strong as Tracy -- a high category 4 cyclone that devastated Darwin, on the northern coast, on Christmas Day, 1974. But Dr Nott said that the most important concern was community vulnerability.

"People here don't believe that they can be hit by a big cyclone," he said. "People can see this as a scare story, but to be scared is to be aware, and awareness is a key issue for urban planners."

"Complacency is one of the biggest problems in planning."

A study by one of Dr Nott's students recently compared the attitudes of people in Cairns with those of Broome, on the north-west coast, after category 2 cyclones threatened the two towns recently.

"People in Broome considered themselves to be very, very lucky that it was only a category 2," he said, "while in Cairns they considered themselves to be very unlucky."

Dr Nott has worked on the study for five years, and recent funding from the Australian Research Council and two insurance companies will see it continue for another three years. He said the study was also contributing to better understanding of the correlation between cyclonic intensity and climate change.

The insurance industry supports the research because it will allow more accurate predictions of future economic loss caused by cyclones.

Climate researchers will be able to use the records to more accurately track climate change, and Dr Nott said that ecologists would now need to consider the significance of more frequent super-cyclones and their impact on tropical rainforests and coral reefs.

"Disturbance by events like cyclones is a major factor in the evolution and diversity of species," he said.

"If severely destructive cyclones are 10 times more common than we thought, we need to see them as forces that may have shaped our natural environment, rather than as rare, freak events."